The invention pertains to methods of forming titanium-based mixed-metal materials and zirconium-based mixed-metal materials. The invention also pertains to sputtering targets, and in particular applications pertains to zirconium-containing sputtering targets and/or titanium-containing sputtering targets.
There are numerous applications in which it can be desired to form mixed-metal products. For purposes of interpreting this disclosure and the claims that follow, the terms xe2x80x9calloyxe2x80x9d and xe2x80x9cmixed-metal productxe2x80x9d are both defined to pertain to compositions having at least two elements present to amounts greater than or equal to the sum of any metallic impurities. For example, a material that is 4N5 pure (i.e., 99.995% pure) has a total of all metallic impurities of 50 ppm or less. A 4N5 alloy (or mixed-metal product) of Ti and Zr is defined herein to comprise both Ti and Zr in amounts greater than or equal to 50 ppm. Typically, one of the Ti and Zr would be present in much higher concentration than the other, but regardless, both would be present in concentrations greater than that of the total metallic impurities. Other exemplary mixed-metal materials are a 3N5 mixed-metal material, which, in accordance with the definition herein comprises at least two elements that are each present to a concentration in excess of 500 ppm; and a 5N5 mixed-metal material, which, in accordance with the definition herein comprises at least two elements which are each present to a concentration in excess of 5 ppm. The percentages and concentrations referred to herein are weight percentages and concentrations, except, of course, for any concentrations and percentages specifically indicated to be other than weight percentages or concentrations.
Among the applications for which it can be desired to form a mixed-metal product or alloy are applications in which it is desired to form ingots of high purity alloys. It can be desired to form ingots of high purity alloys to enable formation of sputtering targets (also referred to as physical vapor deposition targets) from the ingots. The sputtering targets will have uniform distribution of alloys throughout as a result of being formed from ingots consisting of a uniform composition of high purity alloys.
Typically, alloys are made by either adding elemental alloy components to a molten pool of bulk metal, or by pre-mixing and blending various melt feedstock materials with one another before actually melting the materials together. A limitation of the above-described processes is that the processes do not lend themselves to a batch melting process in that at no time is the whole of an ingot material simultaneously molten. Because of this, several consecutive melting operations must be performed in order to form a uniform refractory metal alloy. Without multiple melting operations, variations in chemical composition form in a resulting ingot material. Such variations in chemical composition can lead to problems in structures formed from the ingot materials. For instance, if sputtering targets are formed from the ingot materials, the sputtering targets can have non-uniform chemical compositions reflecting the non-uniform chemical composition within the ingot. If the sputtering targets are utilized in semiconductor fabrication, material will be sputtered from the targets to deposit a film on a semiconductive substrate. Ideally, the film will be homogeneous and uniform across the material. However, variations in chemical composition and homogeneity within a sputtering target can translate into variations in composition and homogeneity of a deposited film, and reduce quality of devices comprising the film.
For the above-discussed reasons, it is desired to develop methodology for forming ingots having uniform and homogeneous composition throughout.
Another aspect of the prior art is that integrated circuit interconnect technology is changing from aluminum subtractive processes to copper dual damascene processes. The shift from aluminum to copper is causing new barrier layer materials to be developed. Specifically, titanium nitride (TiN) films had been utilized as barrier layers in the aluminum technologies to inhibit aluminum atoms from diffusing into adjacent dielectric materials and causing device failure. The TiN films can be formed by, for example, reactively sputtering a titanium target in a nitrogen atmosphere. The TiN films are found to be poor barrier layers relative to copper because the diffusivity of copper atoms through TiN films is too high.
Another problem that can occur in attempting to utilize titanium materials as barrier layers can occur in attempting to adhere titanium materials to dielectric materials. Specifically, it is often found that titanium materials adhere poorly to commonly used dielectric materials (such as, for example, silicon dioxide), and that circuit defects can be caused by such poor adhesion.
In an effort to avoid the problems associated with titanium, there has been development of non-titanium barrier materials for diffusion layers. Among the materials which have been developed is tantalum nitride (TaN). It is found that TaN can have a close to nanometer-sized grain structure and good chemical stability as a barrier layer for preventing copper diffusion. However, a difficulty associated with TaN is that the high cost of tantalum can make it difficult to economically incorporate TaN layers into semiconductor fabrication processes.
Titanium can be a lower cost material than tantalum. Accordingly, it could be possible to reduce materials cost for the microelectronics industry relative to utilization of copper interconnect technology if methodology could be developed for utilizing titanium-comprising materials, instead of tantalum-comprising materials, as barrier layers for inhibiting copper diffusion. It is therefore desirable to develop new titanium-containing materials which are suitable as barrier layers for impeding or preventing copper diffusion, and to develop methodology for forming sputtering targets comprising the new materials.
In addition to the desirability of developing new titanium-containing materials which are suitable as barrier layers, it would also be desirable to develop other materials suitable as barrier layers and having either lower cost or better properties than the tantalum materials presently being utilized. Further, it would be desirable to develop methodology for forming sputtering targets comprising such other materials.
In one aspect, the invention encompasses a method of forming a titanium-based or zirconium-based mixed-metal material. For purposes of interpreting this disclosure and the claims that follow, a xe2x80x9ctitanium-basedxe2x80x9d material is defined as a material in which titanium is a majority element, and a xe2x80x9czirconium-basedxe2x80x9d material is defined as a material in which zirconium is a majority element. A xe2x80x9cmajority elementxe2x80x9d is defined as an element which is present in larger concentration than any other element of a material. A majority element can be a predominate element of a material, but can also be present as less than 50% of a material. For instance, titanium can be a majority element of a material in which the titanium is present to only 30%, provided that no other element is present in the material to a concentration of greater than or equal to 30%. In an exemplary process of forming a titanium-based mixed-metal ingot, such ingot can be formed by combining a mixture of titanium halide and at least one other metal halide with a reducing agent to produce a mixed-metal product. The mixed-metal product is then melted to form a molten mixed-metal material. The molten mixed-metal material is cooled into a mixed-metal ingot. The ingot comprises titanium and at least one other metal. The titanium is the majority element of the ingot, the ingot has a purity of titanium and the at least one other metal of at least 99.95%. The method can be utilized for forming a zirconium-based material by substituting zirconium halide for the titanium halide.
In another aspect, the invention encompasses a method of electrolytically forming a titanium-based mixed-metal material. A mixture of titanium and at least one other metal is electrically deposited as a mixed-metal product. The mixed-metal product is melted to form a molten mixed-metal material. The molten mixed-metal material can be cooled into a mixed-metal ingot. The ingot comprises the titanium and the at least one other metal. The titanium is the majority element of the ingot, and the ingot has a purity of titanium and the at least one other metal of at least 99.95%. The method can be utilized for electrolytically forming a zirconium-based mixed-metal ingot by substituting zirconium for the titanium.
In another aspect, the invention encompasses an iodide transfer method of forming a titanium or zirconium-based mixed-metal material. A mixture comprising either titanium or zirconium is provided in a reaction apparatus with iodine gas and a heated substrate. The titanium or zirconium is reacted with the iodine gas to form an iodide which is subsequently transferred to the heated substrate. Heat from the substrate is utilized to decompose the iodide and produce a mixed-metal product comprising the titanium or zirconium. The mixed-metal product can be melted to form a molten mixed-metal material which can then be cooled into a mixed-metal ingot.
In yet another aspect, the invention encompasses a sputtering target comprising zirconium and one or more elements selected from the group consisting of Al, B, Ba, Be, Ca, Ce, Co, Cs, Dy, Er, Fe, Gd, Hf, Ho, La, Mg, Mn, Mo, Nb, Nd, Ni, Pr, Sc, Sm, Sr, Ta, Ti, V, W, Y, and Yb.
In yet another aspect, the invention encompasses a sputtering target comprising titanium and boron.